Enterprise Systems Connection (ESCON) is generally a fiber optic connection technology that interconnects mainframe computers, workstations and network-attached storage (NAS) devices across a single channel. Typically, ESCON is capable of communication at a rate of 18.6 MB/second over distances of up to 8 kilometers. ESCON was introduced by IBM in 1990 to replace the older, slower, copper-based Bus & Tag channel technology of 1960-1990 era mainframes.
Synchronous optical networking (SONET) and Synchronous Digital Hierarchy (SDH), are generally two closely related multiplexing protocols for transferring multiple digital bit streams using lasers or light-emitting diodes (LEDs) over the same optical fiber. SONET and SDH are typically characterized as pure time division multiplexing (TDM) protocols, offering permanent connections, and do not involve packet mode communication. They are often considered to be physical layer protocols.